Conventionally there have been a large number of techniques implementing force driving vehicles to meet drivers' demands. For example, Japanese Patent Laying-open No. 2006-020481 discloses a motive power output device achieving a good feel for driving. This motive power output device is capable of outputting motive power to a drive shaft. The motive power output device includes: an internal combustion engine; an electric power/motive power input/output means connected to an output shaft of the internal combustion engine and the drive shaft and capable of inputting/outputting electric power/motive power to output at least a portion of motive power from the internal combustion engine to the drive shaft; an electric motor capable of inputting and outputting motive power to the drive shaft; an electricity storage means capable of communicating electric power with the electric power/motive power input/output means and the electric motor; required-driving-force setting means setting the drive shaft's required driving force in accordance with an operator's operation; target motive power setting means setting a target motive power of the internal combustion engine in accordance with the set, required driving force; and drive control means that normally exerts control to drive the internal combustion engine, the electric power/motive power input/output means and the electric motor to output the set target motive power from the internal combustion engine and also output driving force based on the required driving force to the drive shaft, and exerts control in response at least to the target motive power varying in sign to drive the internal combustion engine, the electric power/motive power input/output means and the electric motor to output driving force based on the required driving force to the drive shaft while maintaining the rotation speed of the internal combustion engine before and after the target motive power varies in sign.
The disclosed motive power output device can prevent the internal combustion engine from being operated with its rotation speed different from that which the operator normally expects when the internal combustion engine's target motive power for outputting the required driving force based on the operator's operation varies in sign. As a result a satisfactory feel for drive can be achieved.
The above publication describes setting a shift position that allows a vehicle to manifest engine braking force. As such a shift position, a plurality of stages of shift positions are set to manifest engine braking force in stages in magnitude. In this case, the engine braking force is implemented by setting for each stage a lower limit value for the rotation speed of the internal combustion engine. For example, if a driver operates a shift lever to a low stage, then the lower limit value for the rotation speed is set to increase and accordingly the internal combustion engine has its rotation speed elevated by MG1. This manifests an engine braking effect as intended by the driver.
However, if the internal combustion engine has its rotation speed uniformly elevated regardless of how the shift lever is operated, and the driver shifts between a plurality of stages quickly, the internal combustion engine nonetheless has its rotation speed varied at a uniform rate of change. As such, if the driver quickly shifts between a plurality of stages to manifest larger engine braking force, the internal combustion engine may have its rotation speed varying slower than expected by the driver. This cannot achieve a satisfactorily responsive engine braking effect as intended by the driver.